A polarization multiplexing system is known as a transmission system to speed up an optical communication system. The Polarization multiplexing system is a transmission system in which two pieces of independent data are transmitted at a time by using polarization multiplexed light that is obtained by combining signal light having polarized waves orthogonally intersecting each other.
In an optical transmission device that uses the polarization multiplexing system, an optical modulator that modulates light of a predetermined wavelength is installed. The two pieces of the signal light obtained from light of the predetermined wavelength by being modulated by the optical modulator are combined in a state in which the polarized waves are orthogonally intersected with each other and are output, as polarization multiplexed light, to optical transmission path on the downstream side.
Regarding the optical transmission devices, studies have been conducted on various kinds of technologies that further improve the communication speed. For example, there is a known technology in which a plurality of optical modulators associated with a plurality of different wavelengths is integrally arranged on a single substrate. With this technology, two optical modulators that modulate two pieces of light of different wavelengths are arranged in parallel in the width direction.
Patent Document 1: Japanese Laid-open Patent Publication No. 2001-036505
However, the conventional technology described above is not considered the prevention of damage to optical components while reducing the size of the device in which a plurality of optical modulators is integrally arranged on a single substrate.
This point will be described below. It is conceivable that, in order to integrally arrange a plurality of optical modulators on a single substrate, the width of the substrate is increased. However, if the width of the substrate is increased, a reduction in the size of the overall device is prevented. Furthermore, if the width of the substrate is increased, because the transmission distance of an electrical signal that is used by an optical modulator to modulate light becomes long, the electrical signal is attenuated. As a result, the quality of the signal light that is obtained from the light modulated by using the electrical signal is degraded. To avoid the degradation of the quality of such signal light, the width of the substrate is preferably reduced.
To solve this problem, it is conceivable to use a structure in which optical components called an optical path changing prism are arranged downstream of each of the modulators and the distance of an optical path of the signal light that is output from each of the modulators is increased in the width direction. With this structure, even if the width of the substrate is decreased, it is possible to secure space that is used to arrange another optical component on the downstream side of the optical path changing prism. However, there is a problem in that, as the width of a substrate is decreased, a possibility of damage due to optical path changing prisms being brought into contact becomes high.